text: //请引入 proj4.js 和 proj4leaflet.js
  L.CRS.Baidu = new L.Proj.CRS('EPSG:900913', '+proj=merc +a=6378206 +b=6356584.314245179 +lat_ts=0.0 +lon_0=0.0 +x_0=0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs', {
      resolutions: function () {
          level = 19
          var res = [];
          res[0] = Math.pow(2, 18);
          for (var i = 1; i < level; i++) {
              res[i] = Math.pow(2, (18 - i))
          }
          return res;
      }(),
      origin: [0, 0],
      bounds: L.bounds([20037508.342789244, 0], [0, 20037508.342789244])
  });
  
  L.tileLayer.baidu = function (option) {
      option = option || {};
  
      var layer;
      var subdomains = '0123456789';
      switch (option.layer) {
          //单图层
          case "vec":
          default:
              //'http://online{s}.map.bdimg.com/tile/?qt=tile&x={x}&y={y}&z={z}&styles=pl&b=0&limit=60&scaler=1&udt=20170525'
              layer = L.tileLayer('http://online{s}.map.bdimg.com/onlinelabel/?qt=tile&x={x}&y={y}&z={z}&styles=' + (option.bigfont ? 'ph' : 'pl') + '&scaler=1&p=1', {
                  name: option.name, subdomains: subdomains, tms: true
              });
              break;
          case "img_d":
              layer = L.tileLayer('http://shangetu{s}.map.bdimg.com/it/u=x={x};y={y};z={z};v=009;type=sate&fm=46', {
                  name: option.name, subdomains: subdomains, tms: true
              });
              break;
          case "img_z":
              layer = L.tileLayer('http://online{s}.map.bdimg.com/tile/?qt=tile&x={x}&y={y}&z={z}&styles=' + (option.bigfont ? 'sh' : 'sl') + '&v=020', {
                  name: option.name, subdomains: subdomains, tms: true
              });
              break;
  
          case "custom"://Custom 各种自定义样式
              //可选值：dark,midnight,grayscale,hardedge,light,redalert,googlelite,grassgreen,pink,darkgreen,bluish
              option.customid = option.customid || 'midnight';
              layer = L.tileLayer('http://api{s}.map.bdimg.com/customimage/tile?&x={x}&y={y}&z={z}&scale=1&customid=' + option.customid, {
                  name: option.name, subdomains: "012", tms: true
              });
              break;
  
          case "time"://实时路况
              var time = new Date().getTime();
              layer = L.tileLayer('http://its.map.baidu.com:8002/traffic/TrafficTileService?x={x}&y={y}&level={z}&time=' + time + '&label=web2D&v=017', {
                  name: option.name, subdomains: subdomains, tms: true
              });
              break;
  
          //合并
          case "img":
              layer = L.layerGroup([
                  L.tileLayer.baidu({name: "底图", layer: 'img_d', bigfont: option.bigfont}),
                  L.tileLayer.baidu({name: "注记", layer: 'img_z', bigfont: option.bigfont})
              ]);
              break;
      }
      return layer;
  };